This invention relates to the recovery of hydrocarbons from hydrocarbon contaminated sludge or particulate solid material, for example the recovery of bitumen from bitumen contaminated earth.
In the extraction of bitumen from tar sands, also known as oil sands or bituminous sands, it is well known to use water extraction processes such as a cold water process or a hot water process, a hot water process being commercialized. One of the end products of such processes, in addition to the desired bitumen concentrate, is bitumen contaminated tailings. For various reasons, it is desirable to recover bitumen from such tailings. A process for this purpose is described in U.S. Pat. No. 4,392,941 (Roth et al) issued Jul. 12, 1983, the contents of which are hereby incorporated herein by reference. Roth et al teach a process in which the tar sands sludge, having the bitumen liberated from the tar sand solids, is diluted with water and subjected to high-shear agitation and aeration. The treated sludge is then allowed to settle under gravity to obtain an upper bitumen containing froth layer and a lower sludge layer of reduced bitumen content. Additives can be added to facilitate separation of the bitumen. The Roth et al process is particularly intended for the recovery of bitumen from sludge in a tailings pond to which tailings of a narrow and uniform solid size range from a water extraction process has been fed.
It is also interesting to note the teaching in U.S. Pat. No. 4,410,417 (Miller et al) issued Oct. 18, 1983, the contents of which are also incorporated herein by reference, which is concerned with the problem of separating high viscosity bitumen from tar sands. The teaching of Miller et al is to grind the tar sand to obtain phase disengagement of the bitumen phase from sand phase, and thereafter use flotation techniques to obtain phase separation of the bitumen phase from the sand phase. Phase disengagement is assisted by the use of a suitable wetting agent during the crushing step, while the phase separation step is assisted by the use of a promoter oil in a flotation step. The flotation step is conventional mechanical flotation and involves the attachment of air bubbles to the hydrophobic surface of the bitumen particles.
However, there is also a need for a process to recover bitumen from bitumen contaminated waste comprised essentially of coarse sand, fine sand, clay, gravel or mixtures thereof of a wide variety and range of sizes. Such waste may for example be used drilling mud from an oil well or sand which has been used to mop up an oil spill at an oil production site. Bitumen contaminated drilling mud will ordinarily consist primarily of clay, and bitumen contaminated mop-up sand will of course consist primarily of sand. In both cases, the other solids mentioned above may also be present, and all may be coated with bitumen. Such bitumen contaminated material previously was used to stabilize road surfaces, but for environmental reasons such use is no longer permitted in many areas.
Similarly, there is also a need for a process to recover heavy fuel oil such as Bunker C from oil-contaminated earth, which comprises clay and/or sand compounds, such contamination occurring for example as a result of leakage of fuel oil from a storage tank into the surrounding soil. It is known that such events occur from time to time at locations such as fuel storage stations and possible environmental problems resulting from such leakages are self-evident.
Furthermore, as evidenced by the recent oil spill in Alaska from the oil tanker Valdez, there is also a need for a process to recover heavy fuel oil which has been spilled at sea and has subsequently been washed up on a beach to contaminate the sand thereof.
The teaching of the prior art, such as that referred to above, does not suggest a solution to the problem mentioned above of recovering hydrocarbons from such man-made non-homogenous hydrocarbon-contaminated material.